Proving dead with a PV array and a locked landlord's cupboard
You are to carry out a periodic inspection of a first-floor tenant's distribution board in a 1960s shop parade. The board is fed by a 3-phase 63 A submain from the landlord's intake cupboard, which is locked and shared with three other tenants. The tenant's board has no main switch; the submain is controlled by a 63 A TP&N switch fuse in the landlord's cupboard. On the roof there is a 4 kWp PV system with an inverter connected into the tenant's board through a dedicated 16 A MCB, with AC and DC isolators adjacent to the inverter. A landlord's emergency lighting circuit is also fed from the tenant's board and is not identified on the schedule. The tenant's staff are working in the shop.
1. Set out your isolation procedure from arrival to proving dead.
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- Identify every source before touching anything: the landlord's 63 A TP&N switch fuse, the PV inverter (AC and DC sides), the landlord's emergency lighting circuit fed from the tenant's board, and the other tenants' circuits sharing that cupboard.
- Arrange access and permission for the landlord's cupboard in writing, with a named contact. You cannot isolate what you cannot reach.
- Isolate at the switch fuse. Fit a personal padlock, keep the key, and fix a warning notice. Locking the cupboard door alone is not adequate lock-off.
- Isolate the PV. Open the inverter AC isolator and the DC isolator. The main switch does not make the PV side dead - the inverter can backfeed until anti-islanding operates, and there are live DC parts at the inverter and array.
- Prove the voltage indicator on a proving unit, then test for dead at the point of work: L1–L2, L1–L3, L2–L3, L1–N, L2–N, L3–N, each line to PE, N to PE, and the PV AC side. Prove the indicator again on the proving unit afterwards.
- Only then apply the earth and begin work, and tell the shop staff what is happening and for how long.
2. How do you deal with the unidentified landlord's emergency lighting circuit and the shop staff while the supply is off?
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The emergency lighting is a landlord's service fed from the tenant's board - it is not yours to leave dead without agreement.
- Notify the landlord and the tenant in writing that emergency lighting will be interrupted, and agree a time.
- Confirm what lighting provision remains during the shutdown: battery-backed fittings will run for their rated duration; if there is none, the shop cannot be occupied safely and the work must be scheduled outside trading hours.
- If the circuit cannot be positively identified and isolated, record it as a limitation and note specifically that the emergency lighting circuit was not verified.
- The isolation is under your control: nobody re-energises except you, the work area is screened, and staff are kept clear. If the tenant cannot work around dead circuits, reschedule - the isolation is not negotiable.
3. You cannot get the key to the landlord's cupboard on the day. What do you do?
Read the worked answer
You do not work live, and you do not treat testing around an accessible live board as a substitute for isolation.
- Arrange access. The landlord has a duty to allow safe inspection of the installation serving the building; get a named contact and a date.
- If access genuinely cannot be arranged, the extent shrinks to what can be safely inspected dead - which, for this board, is nothing. Record the limitation precisely: 'Landlord's intake cupboard not accessible; tenant's distribution board could not be isolated; no dead testing carried out on the circuits served from that board.'
- The report must reflect that extent: circuits can be listed and visual findings from the live inspection recorded, but the conclusion must be qualified and the client told in writing that the affected circuits are unverified and a follow-up visit is needed.
- Any C1/C2 items observed on the accessible parts are still recorded. Do not issue a 'satisfactory' report for an extent you have not covered.